1. ISSUE60
CH4
CAN BE
WORTH SO MUCH MORE
The role of oil analysis in gas engine reliability (part 1 of 2)
by Steven Lara-Lee Lumley, N6 Mech.Eng.
It is said that energy is the blood that runs through
the veins of every economy. It is to the survival of an
economy what water is to the survival of the human
body. Without energy, the wheels of the economy
literally do not turn. Energy is consequently a
facilitator of economic development and stability.
According to the South African department of
energy (DoE), energy security within the South
African context means ensuring that diverse energy
resources, in sustainable quantities and at affordable
prices, are available to the South African economy
in support of economic development and poverty
alleviation, taking into account environmental
management requirements.
In considering this definition of energy security, it
is apparent that the mitigation of climate change
through reduced greenhouse gas emissions and the
incorporation of renewable energy into the South
African energy portfolio is also necessary.
In 2008 more than 90% of South Africa’s electricity
was produced from coal, with nuclear energy making
Mrs Steven Lara-Lee Lumley (HND N6 MLA II),
(Technical Development) WearCheck Africa
235MW Aggreko power plant running on natural gas at Ressano Garcia Mozambique – Image courtesey of Aggreko South Africa
WearCheck is a registered ISO 9001, ISO 14001 and ISO 17025 company
Condition Monitoring Specialists

2. 2
up most of the balance. Growing energy demand and concerns over
the environmental impact of coal-fired power generation has led
the DoE to develop programmes like the Integrated Resource Plan
(IRP), the Integrated Energy Plan (IEP) and the Renewable Energy
Independent Power Producer Procurement Programme (REIPPP)
which are all aimed at diversifying South Africa’s energy portfolio
through the incorporation of alternative energy technologies, both
renewable and non-renewable.
These alternative technologies will also include the utilisation of
natural gas and landfill gas for power generation.
Development of regional gas-fields will lead to natural gas becoming
a more significant fuel source in South Africa. With the availability of
natural gas in neighbouring countries like Mozambique and Namibia,
and the discovery of offshore gas reserves in South Africa, the gas
industry in Southern Africa is set to undergo a renaissance.
This notion is further supported by the DoE’s imminent release of its
Gas Utilisation Master Plan (GUMP) which sets the tone for the role
natural gas could conceivably play in electricity output in South
Africa. Natural gas, while not renewable, is an abundant, clean low-
carbon fossil fuel that is projected to become a significant fossil
energy medium in the next fifty years.
Similarly The DoE’s target of incorporating 17.8GW of renewable
energy capacity by 2030 into the South African energy mix also
includes the use of biogas for power generation, albeit to a lesser
extent than the allocations made to other renewable technologies.
So what do these two scenarios have to do with something called
CH4
you might ask? Well, at the heart of both natural and landfill
gas is CH4
.
CH4
is the chemical formula for methane and it is the main
component in natural gas and biogas. Methane is produced by
the breakdown of biodegradable material in landfills, waste water
treatment plants (sewage works), swamps and marshes but is also
found in oil, gas and coal deposits.
Natural gas originates from plant and animal matter which
decomposed millions of years ago and is now located in reservoirs
under the earth’s surface. Natural gas is primarily comprised of
methane with other gases in smaller proportions.
The composition of natural gas can vary significantly from one
location to another. Dry natural gas consists nearly entirely of
methane. Wet natural gas contains less than 85% methane but has
a higher percentage of liquid natural gases (LNGs) such as ethane
and butane. Natural gas can be further classified as sweet or sour
depending on sulphur compounds present in the gas.
The combustion of natural gas produces around 40 to 50% less
carbon dioxide than when coal is burned to produce the same
amount of energy and it is for this reason that it is often referred to
as the cleanest fossil fuel.
Durban solid waste landfill gas to electricity plant courtesey of Clark Energy

3. 3
generation units but can also function as peaking plants to meet
fluctuations in local electricity demand. They can generate
electricity in parallel with the local electricity grid, in island mode
operation, or for power generation in remote areas.
Gas engines operate on similar principles as petrol (spark ignition)
engines but there are some differences in the construction and
operation of gas engines compared with other types of internal
combustion engines. For one thing, gas engines usually operate at a
lower compression ratio and higher combustion temperatures than
the average diesel engines. Added to that, the volumetric efficiency
of gas engines is generally lower than petrol engines because the
volume of the gas required to achieve the same energy output is
considerably larger than that for liquid fuels. This also means that
the gas engine is slower to respond to rapid fluctuations in demand.
In terms of the lubricants they use, the primary difference between
gas engine lubricants and other internal combustion engine oils is
the need to withstand the various levels of oil degradation caused
by the higher operating temperatures, as well as the combustion
process of gas fuels that contain varying impurities depending on
the source and quality of the gas fuel. As a result of these higher
operating temperatures, oil degradation modes like oxidation and
nitration need to be monitored closely. Gas engines also tend to
burn cleaner than diesel engines, with no soot contamination,
which allows their lubricants to be formulated with lower ash levels
and, as they burn gaseous fuel, there is no danger of fuel dilution.
Even though gas engines may differ in many areas, their objectives
in terms of condition monitoring remain the same as that of any
internal combustion engine. Gas engine OEMs acknowledge the
importanceofmonitoringequipmenttoimproveplantreliabilityand
reduce costs, as even the most comprehensive routine maintenance
programme cannot stop faults developing in machinery.
One of the most effective and least expensive condition-
monitoring techniques available to gas engine operators and
OEMs is oil analysis, as it provides a wealth of information about
the lubricant’s condition, contaminants and the mechanical wear
taking place. When oil analysis results are trended over a period of
time, potential problems can be identified and this, in turn, helps
machine-operators schedule the appropriate maintenance and
avoid costly repairs and reduce machine downtime.
In this Technical Bulletin, we will look at what oil analysis can
measure in terms of the first three functions of oil analysis, which
are: to detect abnormal wear, contamination and oil degradation.
Active monitoring of the above provides early warning of abnormal
operating conditions that can lead to catastrophic failures in gas
engines if not detected and corrected.
Detecting abnormal wear
Commercial oil laboratories employ varying techniques when it
comes to detecting (quantifying and classifying) wear particles in
oil, each with its own strengths and limitations. The most widely
used and OEM-requested laboratory techniques will be described
below.
Biogas, on the other hand, is a form of renewable energy produced
from organic matter through a biological process. It is typically
derived from anaerobic digestion or fermentation processes and
can be produced from various organic feedstocks including biomass,
wastewater sludge, agricultural waste and municipal waste. Landfill
gas (LFG) is a type of biogas that is produced from municipal solid
waste.
LFG is a natural by-product of the decomposition of organic
material in municipal solid waste under anaerobic conditions. LFG
consists of roughly 50% methane and 50% carbon dioxide, with less
than 1% of non-methane organic compounds and trace amounts of
inorganic compounds.
Behind the struggle to address global warming and climate change
lies the increase in greenhouse gases in our atmosphere. While
carbon dioxide is typically painted as the bad boy of greenhouse
gases, methane is considerably more potent as a heat-trapping gas
than carbon dioxide, so its prevention of escape from landfill sites
into the atmosphere and its utilisation as a renewable fuel source
for power generation is advantageous.
The search for inexpensive and reliable energy has prompted
interest in natural gas which, in turn, has increased the popularity of
stationarygasengines.Ithasalsoledtothegrowinguseofalternative
gases, such as LFG. As a result of this increased popularity, the use of
gas engines for power generation has become more prevalent and,
with estimates that up to 25% of worldwide electricity demand will
be generated from gas by 2025, this trend seems likely to continue.
But what exactly is a gas engine?
Well that depends on who you ask, but for the purposes of this
Technical Bulletin, a gas engine will refer to a heavy-duty industrial
engine used for power generation or cogeneration which is the
simultaneous production of electricity through the recovery and
the utilisation of heat generated from the engine.
Simply put, a gas engine is an internal combustion engine running on
gas such as natural gas, biogas, landfill gas or coal gas. Gas engines
are generally categorised as two stroke, four stroke and four stroke
duel fuel.
The basic stationary gas engine and generator used for the
production of power consists of four main components – an engine,
a generator, a heat exchanger or heat recovery system and finally a
control system.
Once the gas is burnt in the cylinders of the engine, the force
turns a crank shaft within the engine. The crank shaft turns an
alternator which results in the generation of electricity. Heat from
the combustion process is released from the cylinders. The released
heat is either recovered and used in a combined heat and power
configuration (CHP) or dissipated via radiators. Lastly, there are
electronic control systems which manage the whole process to
ensure optimum performance of the generator set.
Gas engines are normally operated as stationary continuous

4. 4
Spectrometric analysis
The spectrometer is used to determine the presence and
concentration of different elements in the oil. These are
measured in ppm (parts per million). This is a very small unit
and 1 ppm = 1/10 000th of 1%. The measured elements are
usually divided into three broad categories: wear metals such
as iron, contaminants such as silicon and oil additives such as
calcium.
Another important function of oil analysis is to verify the oil
in use and this can be done by comparing the physical and
chemical characteristics of the in-service lubricant to those of
the unused product. The spectrometer is one of the laboratory
tests that can be used to verify the oil in use as it measures the
concentration of additives in the oil.
This is an important function in any application, but especially
in gas engines, as the formulation of a gas engine oil is a
delicate balancing act that hinges on ensuring that the correct
concentration of additives is present in the oil, while at the
same time limiting the resultant ash content of the oil.
Since every engine burns a small amount of lubricating oil,
and since many types of alkaline additives are ash-producing
when burnt, they contribute to the formation of ash deposits
in the combustion chamber. As natural gas engines can burn
large quantities of lubricating oil during operation, engine
manufacturers limit the amount of ash-producing additives in
the oil.
The ash is the portion of the lubricant that is left behind as
a deposit after complete burning of the oil during operation.
It is a whitish-grey deposit and comes from calcium and
magnesium containing detergent additives. The amount of
ash deposits that form in an engine is related to a lubricant’s
formulation and oil consumption of the engine.
Gas engines do not produce soot and there is no liquid fuel to
help lubricate the intake and exhaust valves. As a result of this,
gas engines are dependent on the lubricant ash to provide
lubrication between the hot valve face and its mating seat.
Too little ash can accelerate valve wear, while too much ash
may lead to valve guttering and subsequent valve torching.
Added to this, excessively high concentrations of certain zinc
or phosphorus containing anti-wear additives can also be
harmful to catalyst-equipped natural gas engines, as these
additives may deactivate the exhaust catalyst by forming
glassy-amorphous deposits which prevent the exhaust gas
from reaching the active surfaces of the catalyst, which in turn
impairs the catalyst’s ability to control harmful emissions.
Ensuring the correct oil in use can help minimise downtime as
a result of unscheduled maintenance and ultimately promote
optimal engine performance.
Unfortunately, the spectrometer can only measure very small
particles in the oil, usually less than eight microns in size. The
instrument cannot “see” larger particles that might indicate
that a severe wear situation is developing. It is for this reason
that the following two tests should also be performed as part
of a standard gas engine oil analysis programme.
PQ (Particle Quantifier)
The PQ index or ferrous debris monitor provides a measure
of the total ferrous content of the oil sample and from this
measurement, the total amount of ferrous (iron) debris can be
determined irrespective of the particles’ size.
Wear metal particles detected by spectroscopy are typically
less than eight microns in size. These small particles can be
generated by benign rubbing wear. Larger particles are
From left to right pictures of a good valve, a torched valve and a recessed valve courtesy of Infinium International Limited

5. 5
generated by more severe wear modes such as fatigue wear,
cutting wear and sliding wear. These larger ferrous particles
present in the used oil sample can be detected by using the
PQ method.
MPE(MicroscopicParticleExamination)
In terms of wear particles, their morphology and quantity
provide direct insight into overall engine health.
An MPE is performed by filtering the oil through a membrane
patch of a known micron rating and any debris present
is examined under a microscope. The membrane patch is
examined for wear, contamination and colour.
An MPE can provide clues to the source of the debris and
the potential severity of a problem that may be causing it.
The individual particles themselves are not categorised, but
instead observations are recorded for trending purposes using
a size and concentration reference matrix.
Detect contamination
The third major function of oil analysis is to monitor levels
of contamination. Contaminants can be classified as either
internal or external. Internal contaminants are generated
within the mechanical system, such as fuel dilution and by-
products of combustion, like soot, in the case of a diesel
engine. However, because gas engines tend to burn cleaner
than their diesel counterparts, they do not produce soot and
as the fuel used is gaseous in nature, fuel dilution is not a
concern.
External contaminants are substances that exist in the
environment but should not be in the oil. The most common
ones are dirt and water. Contaminants can be directly
damaging to the machinery being lubricated; dirt is abrasive
and can cause components to wear abnormally; and water
causes metals to rust. Contaminants can also cause the oil
to degrade which, in turn, may have an adverse effect on a
mechanical system.
Siloxanes
Silicon detected in the oil by the spectrometer can have
many sources – as a wear element, air-born dust, additive,
or silicone-based gasket compounds. However, in engines
running on biogas, the silicon detected in the oil could also be
a combustion by-product.
New and siloxane coated piston courtsey of Clark Energy

6. 6
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You might not have heard of siloxanes (silicone-containing
compounds), but there is no doubt that you have come across them
in your everyday life. They play an important behind-the-scenes
role in our daily lives; they wash our hands, brush our teeth, clean
our clothes and even print our newspapers.
Siloxanes are most widely used in the cosmetics industry but are
also used in the manufacturing of plastic products and even in
the food industry as an oil substitute to create low-kilojoule food
products for the diet-conscious.
When siloxane-containing products are disposed of into anaerobic
treatment systems, they volatilise into the biogas.
These siloxanes are found with the methane and carbon dioxide
produced from the decomposing organic matter in anaerobic
digesters and at landfill sites, and contaminate the gas which is used
to fuel engines for power generation.
Biogas and landfill gas can contain one or more species of siloxanes
depending on the organic feedstock used to produce the gas. When
these gases are burned as fuel in gas engines, deposits of solid
silica or silicates will adhere to the cylinder heads, pistons and heat
exchanger surfaces, causing a variety of problems.
These piston and cylinder head deposits are very abrasive, reduce
clearances between the piston ring and liner, and subsequently
alter the compression ratios, resulting in unburned fuel which can
cause damage in severe cases through back-firing, but generally
contaminates the exhaust gas and increases undesirable emissions
to the atmosphere.
Siloxane damage can be severe, causing unscheduled maintenance,
reduced generation capacity, increased operating costs and
ultimately engine failure. It is for this reason that many gas OEMs
recommend direct monitoring of silicon build-up in the engine oil.
Water
Water can exist in three phases in oil: dissolved, emulsified and free.
Different oils have different water-contamination handling abilities
depending on the base stock and additives used during formulation.
The amount of water an oil can carry in solution is known as the
saturation point. Once this point is reached, any additional water
added will form an emulsion or fall out of suspension as free water.
Water is one of the most destructive contaminants in a lubricant and
can cause a wide range of operational problems and significantly
affect engine reliability and longevity. It causes additive depletion,
base oil oxidation and impairs the oil’s film strength. Water
contamination also sharply increases the corrosive potential of
acids found in gas engine oils.
Water contamination of gas engine oils usually leads to the
formation of an emulsion, which reduces the overall usefulness
of the oil. Water leads to increased wear and ultimately reduced
engine life.
In the next instalment of this two-part Technical Bulletin, we will
be detailing which oil analysis techniques can be used to detect oil
degradation of gas engine oils.
Information correct at time of going to print. Sharon Fay Public Relations 04/2015